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India battles to eradicate major crop pest

By
DEVINDER SHARMA in
DELHI

Indian scientists are gearing up for a massive campaign to kill an insect
ravaging the country’s crops. But they are divided over the strategy to
control the American bollworm (Heliothis armigera), which is devouring crops
at a rate of $500 million a year. The pest poses the biggest single threat
to India’s agriculture.

One of the country’s leading entomologists, Kailash Narain Mehrotra,
of the Indian Agricultural Research Institute in New Delhi, wants the government
to pass a law restricting the spraying of cotton with pyrethroid insecticides.
He argues that the insect’s growing immunity to pyrethroids is being caused
by indiscriminate use. Meanwhile, the Indian Council of Agriculture (ICAR)
has drawn up a battle plan to control the pest by biological means, using
its natural enemies.

The bollworm is not new to India, but its status as a pest has grown
enormously. It has eaten its way south to Tamil Nadu and west to the Punjab.
The bollworm is the larva of a small moth. It damages the boll, or fruit,
of the cotton plant. However, it also feeds on other plants in India, such
as chick pea, pigeon pea, sunflower, sorghum and maize.

Mehrotra is alarmed by how fast the insect has become immune to pyrethroids,
first reported in 1988. He says resistance has multiplied at least 100-fold
over the past two years. One pyrethroid pesticide, cypermethrin, failed
to control the pest in an area of Andhra Pradesh 200 kilometres by 75 kilometres.
Resistance has now been reported in the Punjab, Haryana, Gujarat and Maharashtra.

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At present, farmers spray more than a dozen times in the north and nearly
two dozen times in the south each year. Mehrotra wants pyrethroids restricted
for much of the year and for farmers to use more potent agents, such as
endosulphan, instead.

The ICAR, meanwhile, has started mass production of natural enemies
of the bollworm. These include nuclear polyhedrosis virus (NPV), and parasitic
wasps of the Trichogramma family, which feed on the insect.

The council claims that in gram, which is widely grown in India, biological
agents such as NPV were ‘quite successful’ against the bollworm last year.
‘Gram production has gone up by 10 per cent,’ according to a senior official.
But it remains to be seen whether the biological agents will be effective
in cotton.

‘To ensure adequate and timely supply of the bio-agents to farmers,
as many as 30 mass multiplication units in 11 states have been set up,’
said Rajendra Singh Paroda, deputy director-general of crops, at the ICAR.
The council has identified areas where the bollworm is most active and it
has prepared management packages for various crops.

Paroda agrees that indiscriminate and excessive use of pyrethroids has
boosted the fortunes of the bollworm and elevated minor pests such as aphids
and termites, which have also grown resistant, to the level of major pests.

The ICAR and the International Crops Research Institute for the Semi-Arid
Tropics in Hyderabad have both boosted their research into the insect and
its habits. The international institute has found that the insect’s wide
choice of food allows it to travel easily over great distances and to survive
from one crop season to another.